JP3197837B2 - Digital video recorder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital VCR (video cassette recorder) for recording and reproducing an MPEG2 (Moving Picture Experts Group 2) signal, which is an international standard for image compression, as digital data on a recording medium such as a magnetic tape. About.

[0002]

2. Description of the Related Art MPEG coding employs motion compensated prediction, DCT and entropy coding, and the types of frames are I picture, P picture, and B picture depending on the time axis prediction method as shown in FIG. Pictures are classified into three types.

[0003] An I picture is an intra-frame coded image, and a single frame can be reconstructed using I picture data alone. The P picture is an inter-frame prediction coded image predicted from a temporally preceding I picture or P picture, and the B picture is a inter-frame predicted coded image from a temporally subsequent and preceding I picture or P picture. .
Therefore, in order to reconstruct both the P and B pictures,
We need the data of the frame on which those predictions are based,
One frame cannot be reconstructed using only P and B data alone.

Further, since the data amount of each picture is not fixed, the position on the tape and the position of the image are irrelevant.
However, for example, in the case of a video having a frame rate of 30 frames per second, data for 30 frames per second on average is required for I, B, and P.

Here, for example, consider a case where MPEG data having a frame rate of 30 frames per second is recorded on a digital VCR (hereinafter simply DVCR) based on the HD Digital VCR Council standard.

First, a simple format of the DVCR will be described.

FIG. 7 shows a recording format on a magnetic tape of this standard. The tape records 300 tracks of data per second. Each track is composed of an ITI area composed of insert information and track information, an audio data area, a video data area, and a subcode data area in the order of recording.

Data such as audio and video is recorded in units called sync blocks. As shown in FIG. 8, the sync block includes a sync area (2 bytes), an ID,
It consists of an area (3 bytes), a data area (77 bytes) and a parity area (8 bytes), for a total of 90 bytes.

However, in the case of MPEG data, it is recorded only in the video data area. The video data area has an area of 135 sync blocks. As shown in FIG. 9, it is divided into a data area for normal reproduction (NP data area) and a data area for special reproduction such as high-speed reproduction (TP data area). The TP data area is divided into a TPH data area and a TPL data area according to the reproduction speed.

The reason why the TP data area is provided will be described. If there is no TP data area, all NP data is recorded in the video data area. At this time, if playback is performed at a speed different from that at the time of recording due to a request for fast-forward playback or the like, the head travels over a plurality of tracks, and as a result, MPEG data can only be partially acquired.
MPEG data is only P-pictures and B-pictures described above.
Since an image cannot be reconstructed and an I-picture cannot be reconstructed using only fragmentary data alone, it is necessary to always acquire all I-picture data. In order to reliably obtain an I-picture, the position traced by the head when reproduced at a specific double speed as shown in FIG.
An area from which data can be read is secured in the track as a TP data area. In addition, the TPH data area and the TPL data area are provided separately to provide variations in the playback speed. The TPH area is intended for relatively high-speed playback, and the TPL area is for relatively slow special playback. .

The MPEG data input to the DVCR is recorded by mapping two MPEG transport packets to five sync blocks as shown in FIG. At that time, VC
MPEG at the same timing as when MPEG data was input to R
In order to output data and avoid temporal inconsistency in MPEG data, MPEG transport packets
The time of arrival at the VCR is recorded simultaneously as a time stamp.

The method of trick play will be specifically described with reference to FIG. In FIG. 10, the horizontal rectangles represent one track. For trick play, trick play data is written in a specific area of each track as shown in FIG.
This is achieved by reading the special reproduction data written when the tape is reproduced at a constant speed without any loss. For example, FIG. 10A shows the head trajectory when the tape is fed at a speed 18 times the normal speed, and the data 1 to 6 for special reproduction can be read without loss.

To create special reproduction data, a program to be recorded is first selected from a broadcast bit stream. After extracting a partial I picture of the image from the bit stream of this program and controlling the code amount so as to fit in the data area for special reproduction, an MPEG bit stream for special reproduction is created. This is divided so as to fit in the special reproduction area shown in FIG. 10, and is recorded in each special reproduction area.

In FIG. 10, the same data, for example, 1 is repeatedly recorded. This is because the head trajectory can be read even if it starts from a track other than the illustrated track. Also, FIG. 10A shows the case of 18 × speed, in which all data from 1 to 6 can be read in one scan of the head, but if the data is read in a plurality of scans, the speed is lower than 18 × speed. However, if the conditions are met, all data can be captured. In this case, all data can be captured at speeds of ± 1.5, ± 2.5, ± 8.5 times. In FIG. 10, (a) shows a state where the trick play data is scanned at another double speed.

[0015] As described above, MPEG such as digital broadcasting
In a VCR that records data, the MPE for special playback
A G bit stream is separately created, and divided into portions that are traced by the head at a tape feed speed for special playback such as fast forward, and recorded. During special playback, the G bit stream is read without loss and an MPEG bit stream for special playback is read. By reproducing and inputting this to an MPEG decoder such as a digital broadcast receiver, special reproduction such as fast forward can be performed.

[0016]

By the way, in the above-mentioned prior art, fast-forward playback is possible for video, but no consideration is given to fast-forward playback of audio. Did not. Therefore, the present invention incorporates audio data into the MPEG bit stream for special reproduction, and enables audio reproduction even during special reproduction such as fast forward.

[0017]

According to a first aspect of the present invention, there is provided a digital data recording / reproducing apparatus for recording MPEG data on each track on a tape, wherein a first data is recorded on the track. An area and a second area for recording special reproduction MPEG data, and at the time of special reproduction, outputting the special reproduction MPEG data read from the second area, wherein the special reproduction data is The digital video recorder comprises special reproduction data for video and special reproduction data for audio.

According to a second aspect of the present invention, in the first aspect, for the special reproduction data for audio, the speed of the special audio reproduction is set in advance, and only the audio data is extracted from the input MPEG data and decoded. After performing time compression corresponding to the reproduction speed, MPEG audio encoding is performed again to create special reproduction data for audio.

According to a third aspect of the present invention, in the case of reproducing at the special reproduction speed assumed at the time of recording according to the second aspect, the reproduced special reproduction audio signal is output as it is, and the special reproduction speed assumed at the time of recording is reproduced. If the special playback is performed at a speed other than the above, only the special playback audio signal is extracted from the played special playback data and decoded, and the time axis is calculated based on the ratio of the playback speed assumed during recording to the actual playback speed. This configuration is characterized in that compression and decompression are performed, MPEG audio encoding is performed again, and then output.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a recording side of a digital VCR embodying the present invention.

Bit stream (transport stream: TS) from a digital broadcast tuner (not shown)
(A) is input to the VCR. Usually, a plurality of programs are multiplexed in this TS, and only the TS of a specific program to be recorded is extracted by the program extracting circuit 1. This operation is an operation performed by a normal digital broadcast receiver, and will not be described in detail here.

Output from the program extracting circuit 1 (A)
Are multiplexed with video and audio or accompanying data of data of a specific program to be recorded. The data of this specific program is data (NP data:
The data is written to the buffer 2 for recording as normal play data) by the VCR.

On the other hand, special reproduction data other than the normal speed, for example, TP (trick play) data is simultaneously created as data for fast forward.

Next, the operation of the video data of the TP data will be described.

Since the output (a) of the program extracting circuit (1) is multiplexed with video, audio and other accompanying data as described above, the video data extracting circuit (3) outputs the video from the output signal (a) from the output signal (a). Only data is extracted, and data (c) including only a video signal of a specific program is output. The data area for special playback is limited as described in the conventional example, and it is necessary to record data repeatedly. Therefore, the data amount per recording time compared to the original video data amount Need to be reduced.

For this reason, I-Pictur in video data is usually used.
After extracting only e, the data amount is reduced so that the data amount is smaller than the writable TP data amount as compared with the data amount writable to the TP data. As a method of the reduction, a method of using only some of the extracted I-Pictures and discarding other I-Pictures,
Alternatively, a method of reducing a data amount of one I-Picture by discarding a portion corresponding to a high-frequency component of a video signal in the I-Picture, or a combination of the two is considered.

In this embodiment, in order to record audio data in addition to video data in the TP area, the ratio between the video signal and the audio signal in the TP area is determined in advance, and the TP data amount of the video signal is reduced. Of the total TP data volume,
Limit the data amount to less than the data amount allocated to the video signal.

The TP video data (d) created in this way is stored in the video signal buffer 5.

Next, the audio signal extracting circuit 6 extracts only audio data from the data (a) of the specific program to be recorded and outputs an audio signal (e) of the specific program to be recorded.
Next, the signal (e) is a voice trick play data creation circuit 7
Is input to

The operation of the creation circuit 7 will be described with reference to the detailed block diagram 3 therein.

In FIG. 3, reference numeral 41 denotes an MPEG audio decoding circuit which decodes encoded audio data in the MPEG data into original audio data (e). The audio data restored to the original audio data is input to the N-times speed time compression circuit 42. Here, N is the tape double speed assumed when performing the audio special reproduction. As described above, when the data areas 1 to 6 (see FIG. 10) of the tape format of this embodiment are used, the maximum speed is 18 times. In addition, special reproduction of ± 1.5, ± 2.5, ± 3.5, ± 4.5, ± 5.5, ± 8.5 times is possible. Here, the operation when N = 2.5 will be described as an example.

In the N-times time compression circuit, the time axis is time-compressed to 1 / N. Here, since N = 2.5, for example, a 10-second sound is time-compressed to 4 seconds. As for the time compression method, a technique used in an analog VTR or the like and a tape recorder already in practical use can be used as it is.

As an example of this method, when there is an audio signal of one second as shown in FIG. 4A, the silent part is first deleted to create an audio signal without a silent part as shown in FIG. 4B. I do. Here, if this length becomes 0.6 seconds, a part of the audio signal is discarded to further compress this to 0.4 seconds.
Create a 0.4 second audio signal. By compressing the time axis in this manner, a time-compressed audio signal whose content can be grasped can be obtained without changing the pitch of the audio, although some parts are discarded.

The time-compressed audio signal (S) obtained in this manner is encoded again by the MPEG audio encoder 43 into MPEG audio. At this time, like the TP video signal, the encoding is performed by limiting the TP data amount of the audio signal to be equal to or less than the data amount allocated to the audio signal out of the total TP data amount.

The TP audio data that has been time-axis-compressed and MPEG-encoded is stored in the buffer 8. Here, it is multiplexed with the TP video data created as described above to become TP data (S).

The TP data is input to the track data multiplexing circuit 9 together with the NP data, and the NP data is stored in a predetermined area of the track so as to form the data area of the track shown in the track diagram of FIG. And TP data are assigned with numbers and multiplexed to create track data (G).

The track data is added with an error correction code for recording by an error correction code adding circuit 10 and is formatted by a tape formatting circuit 11.
The signal is amplified by the recording amplifier 12 and recorded on the tape T from the head 13.

Next, the operation at the time of reproduction will be described with reference to the reproduction circuit of FIG.

The signal recorded on the tape T is transmitted to the reproducing head 2
After being read from 0 and amplified by the reproduction amplifier 21, the reproduction signal processing circuit 22 performs signal processing at the time of reproduction such as demodulation, synchronization signal detection, and data separation, and then inputs the error correction circuit 23. The error correction circuit 23 can almost completely correct an error at the time of reproduction using the error correction code added at the time of recording.

The output of this error correction circuit is shown in FIG.
The NP data and the TP data shown in FIG. During reproduction at a normal tape speed, the NP data separated by the TP / NP separation circuit 24 is written into the buffer memory 25, and this is selected by the switching circuit 26 and output to the digital broadcast receiver as a VCR output. I do. This is the same as the MPEG data (a) after the program is selected by the recording side circuit in FIG. 1, and if this is input to the digital broadcast receiver, the digital broadcast receiver
The EG data is decoded and the program recorded on the tape can be viewed.

Next, the operation at the time of special reproduction such as fast forward will be described. In the case of fast-forward, the head scans across the track. Also in this case, the data for NP and the data for TP are mixed and reproduced. Error correction is performed in the same manner as in normal reproduction, and the data is separated into NP data and TP data by the separation circuit 24 in the same manner.

First, only the video signal portion in the TP data is extracted from the TP data by the video signal separation circuit 27 and stored in the buffer 28. This data is composed only of I-Picture that has already been MPEG-encoded. By adding the data of a higher layer later and inputting it to a digital broadcast receiver as it is, it is possible to view an image of special reproduction. it can.

On the other hand, for the audio TP data, only the audio TP data is extracted from the TP data (T) by the audio data separation circuit 29. T for this voice
Since the P data is created assuming the reproduction speed at the time of recording, if the P data coincides, the data can be directly reproduced as an MPEG-encoded audio signal into the digital broadcast receiver to reproduce the audio even during special reproduction. If 2.5x speed is set as an example at the time of recording, at the time of special playback at 2.5x speed, the separated TP audio signal is the same as the TP video signal,
If the data of the higher layer is added later and the data is input to the digital broadcast receiver as it is, the sound at the time of special reproduction can be heard.

As described above, when the data areas 1 to 6 (see FIG. 10) of the tape format of this embodiment are used, the maximum speed is 18 times, and in addition, ± 1.5, ± 2.5, ± 3.5,
Special reproduction of ± 4.5, ± 5.5, ± 8.5 times is possible. As described above, when the double speed at which sound can be reproduced during recording is set to, for example, 2.5 times, other double speeds, for example, 3.5, 4.5, ... 8.
The audio at the time of 5 × speed can be made possible by performing compression / expansion in the audio signal compression / expansion block 30. The inside will be described with reference to FIG.

The TP audio data is input to the MPEG audio decoding circuit 51 and is restored to an audio signal. This audio signal is an audio signal encoded for 2.5 × speed in the present embodiment. At this time, assuming that the fast-forward speed is 4.5 times, the audio compression / expansion circuit 52 compresses the time to the ratio between the assumed speed at the time of recording and the actual reproduction speed, here 2.5 / 4.5. The specific method of this compression is the same as that described at the time of recording. The output from the audio compression / expansion circuit 52 is MPEG-encoded again by the MPEG audio encoding block 53, and is output and stored in the buffer 31.

Of course, when reproducing at the same speed as the double speed assumed at the time of recording, that is, at 2.5 times speed, it is not necessary to perform such compression / expansion processing, so that the switch SW54 is switched to buffer the TP audio signal as it is. Just write it to

If the audio special reproduction is limited to only the set double speed, there is no need to perform the audio compression / decompression processing during reproduction. In this case, the audio data may not be output to the digital broadcast receiver except at the set double speed.

[0049]

According to the present invention, the time-compressed audio signal corresponding to the set fast-forward speed is multiplexed and recorded on the special-reproduction video signal in the special-reproduction data area for fast-forward or the like. MPEG video signals and audio signals can be output to the TV receiver, and audio can be heard even during special reproduction.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a recording side of a digital VCR according to an embodiment of the present invention.

FIG. 2 is a circuit block diagram on the reproduction side of a digital VCR according to an embodiment of the present invention.

FIG. 3 is a detailed block diagram of a voice TP data creation circuit.

FIG. 4 is a diagram for explaining a voice compression method.

FIG. 5 is a block diagram showing details of an audio signal compression / decompression block.

FIG. 6 is a diagram showing a picture structure of MPEG.

FIG. 7 is a diagram showing a recording format of a DVCR.

FIG. 8 is a diagram showing a configuration of a sync block.

FIG. 9 is a diagram showing a track block of a DVB signal.

FIG. 10 is a diagram showing an arrangement position of special reproduction data.

FIG. 11 is a diagram illustrating five sync block units of the DVB signal recording format.

[Explanation of symbols]

 1 Program extraction 6 Audio extraction 7 Audio TP data creation 8 Buffer

Continuation of the front page (72) Inventor Masahiko Tomikawa 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-7-322192 (JP, A) JP-A-9- 261593 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 5/782 H04N 5/91-5/956 G11B 20/10, 20/12

Claims (1)

(57) [Claims] 1. A digital data recording / reproducing apparatus for recording MPEG data on each track on a tape, a first area for recording MPEG data for normal reproduction on said track, and a special area for special reproduction. An apparatus for forming a second area for recording MPEG data and outputting special reproduction MPEG data read from the second area during special reproduction, wherein the special reproduction data is It is composed of special reproduction data for video and special reproduction data for audio. When reproducing at the special reproduction speed assumed at the time of recording, the special reproduction data for audio is output as it is and is assumed at the time of recording. When performing special reproduction at a speed other than the special reproduction speed, the special reproduction data for audio is decoded, and the time axis is compressed and decompressed at the ratio of the reproduction speed assumed at the time of recording to the actual reproduction speed. ,
A digital video recorder characterized by outputting MPEG audio data again.